1. Field of the Invention
The invention relates to printing machines, and more particularly to an image data-oriented printing machine.
2. Description of the Related Art
Observations are already known which relate to preparing the data used for the printing process such that the printing process is optimized. Attempts have been made to make the observed information useful to the printing process. In this case, for example, the intention is for the preparation of the printing image information for the production of the printing plate to be performed in a manner optimized to the printing machine in the process referred to as the pre-press stage. This process, by its nature, is dependent on the availability of information relating to what is to be done later with the image data in the printing machine. Using this information, the printing process can compensate for the changes to the information which are specific to the printing machine in order to achieve good results. This requires communication between the pre-press stage and printing machine. This data interchange is generally achieved by means of so-called print-run standards, which predefine a bandwidth within which a printing machine varies the image data to be printed when specific ink and paper classes are being used. The properties of the pre-press stage and of the printing machine determine the achievable bandwidth. Naturally, it is also possible for special standards to be predefined externally by the printer and, for example in package printing, for these standards to define other transfer characteristic curves which are specifically suitable for this. However, these particular characteristic curves can intrinsically apply only within the very limited range of action in accordance with the defined printing material. In order to improve the print quality in the sense of better agreement with the predefinition and with more highly constant printing results, it is expedient to allow information relating to the product to be printed to influence the quality management system. These days, this information is provided almost exclusively by the printer who operates the machine, with the assistance of special sensors, such as an electronic plate scanner.
Although the product information is present at the pre-press stage, it is to some extent varied when it is output to the printed image carrier (printing plate or printing material). However, the printing machine control system would be able to operate better with the respective product information from the pre-press stage if these variations were known.
It transpires that it is expedient to obtain information for the printing machine control system in general terms from the data which is present at the pre-press stage. For this purpose, these variations would also have to be known at the pre-press stage. The paper "L'integration dans la chaine graphique" (Integration in the graphic chain), presented by J. Schneider at the "Collogue Caractere" (Character conference), 14/15.11.1990, Paris, has already disclosed the practice of feeding image data values which are used to set up the printing plate to the central control station of the printing machine. They can thus be used, for example, for pre-setting the inking zones. EP 0 495 563 A2 proposes using an integrated, computer-controlled system as a control system for a number of stages in a printing process. The information to be applied to the printing plate is present in digital form (digital pre-press) and from this layout information is used to produce, for example, pre-setting data (ink feed) for the printing machine and desired values for the ink feed in order to achieve an envisaged printing characteristic curve.
DE 43 28 026 A1 discloses a communication method in a communication system with computer-controlled data transmission for the purpose of controlling the printing process of a printing machine. This method has been optimized to the effect that, for areas of the printing process which operate upstream of the printing machine, no special adaptation has to be undertaken when different printing machines are used, and that the printing machine is able to receive data relating to the pre-setting and process control without the machine having to know the type of the independently operating area. In this communication method, a communication structure is used for interlinking areas of the printing process which operate on a digital basis and independently of the printing machine, especially areas of a pre-press stage. The communication structure permits the entire printing plate to be imaged, and permits an interchange of data between the various independently operating areas and the printing machine on the basis of which data requests in both directions can be attended to in a manner which is not type-specific. Data for regulating the printing machine is obtained from data which is independent of machine type, and in particular from the pre-press stage. This data can be used by the pre-press stage of the printing machine to influence the data to be printed.
On the other hand, DE 196 27 459 A1 discloses a printing machine in which measured color values are determined with the aid of an image recording device at a large number of measurement locations trailing the printing image. The color valves are transformed into color loci in a defined color space. The distribution of the color loci in the color space is determined, and from this distribution, signals are derived which contain the color loci of the printing ink (CMKY) which was probably used. The derived color loci of the printing inks (CMKY) probably used are in each case compared with the color loci which the operator has preselected. If a color offset resulting from the comparison exceeds a predefined amount, a signal is generated, and a display is activated which contains information for the operator relating to the fact that the laws he has selected probably do not correspond to the printing inks (CMKY) used.